The objective of the proposed research is to determine what factor(s) directs the bi-potential gonad and gonaducts to differentiate according to their genetic sex. Studies will be conducted to isolate substances from fetal plasma and gonads that will alter duct or gonad development. Both in vivo and in vitro bio-assay systems will be used to determine if substances can be isolated with the potential to either stimulate or inhibit development of any segment of the fetal reproductive tract. These substances will then be injected into fetal sheep to induce the freemartin condition.